1. Field of the Invention
The embodiments disclosed herein relate to an inverter apparatus, a method of controlling the inverter apparatus, and an electric motor drive system.
2. Description of the Related Art
Hitherto, there is known a winding switching method enabling operation in a wide range from a low speed area to a high speed area by switching armature windings of an AC electric motor.
Japanese Patent Application Laid-open No. Hei 5-3694 discloses a variable speed driving method involving switching winding connection of a synchronous electric motor by an inverter apparatus used for vehicle driving or the like, in which stable driving is achieved by setting a hysteresis region in switch timing of the winding connection. Specifically, in the above-mentioned variable speed driving method, switch timing from a star connection to a delta connection is set to a speed level Vo (base speed N1), while switch timing from the delta connection to the star connection is set to a speed level Vo′ lower than Vo, and thus the hysteresis region is set in the switch timing.